Silicone HCR (HCR/HTV)
Grade
also PDMS, LSR
Pick for extruded profiles, tubing, calendered sheet and low-volume compression-molded gaskets.
Values for the HCR condition
Other Silicone grades and fills
Silicone is listed in 15 conditions; see the grade overview at Silicone.
Compare all 15 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Sponge/Foam | Pick for low-closure-force weather seals, cushioning and insulation in enclosures and ovens. | — | 2 | 150 | 25 Shore A |
Electrically conductive silicone | Pick for EMI gaskets, grounding pads and ESD-safe seals combining shielding with environmental sealing. | — | 3 | 120 | 20 Shore D |
Thermally conductive (alumina / boron nitride filled) silicone | Pick for thermal interface pads, gap fillers and potting where heat must be moved but electrical isolation kept. | — | 3 | 120 | 18 Shore D |
RTV-2 / Cast PDMS | Pick for prototyping molds, microfluidic PDMS chips, potting and encapsulation where no heated press is available. | — | 6 | 350 | 8 Shore D |
soft grade | Pick for soft-touch skins, low-force seals, membranes and conformal cushions. | — | 7 | 650 | 6 Shore D |
heat-stabilized (iron oxide / rare-earth) silicone, 250–300 °C capable | Pick for oven gaskets, exhaust/turbo seals, ironing and heater components where continuous service exceeds 200 °C. | — | 7 | 350 | 15 Shore D |
flame-retardant silicone (UL 94 V-0) | Pick for rail, EV battery and appliance parts needing UL 94 V-0 with low smoke and halogen-free formulation. | — | 7 | 350 | 16 Shore D |
soft-medium grade | Pick for baby-care parts, low-compression-force gaskets and flexible tubing. | — | 8 | 550 | 9 Shore D |
HCRThis page HCR/HTV | Pick for extruded profiles, tubing, calendered sheet and low-volume compression-molded gaskets. | — | 8 | 400 | 15 Shore D |
Fluorosilicone, fuel and oil resistant | Pick when silicone-level cold flexibility is needed together with resistance to fuels, hydrocarbon oils and solvents. | — | 8 | 250 | 16 Shore D |
general purpose grade | Pick as the default all-round hardness for O-rings, keypads and static seals. | — | 9 | 450 | 12 Shore D |
Liquid silicone rubber, 2-part platinum cure, injection molded | Pick for high-volume automated injection molding of thin, flash-free, dimensionally precise parts. | — | 9 | 550 | 12 Shore D |
medium-hard grade | Pick for dynamic seals, grommets and parts needing better set resistance and extrusion resistance. | — | 9 | 400 | 15 Shore D |
extra-hard grade | Pick for rollers, back-up rings and parts resisting extrusion under high clamp loads. | — | 9 | 220 | 30 Shore D |
hard grade | Pick for high-pressure gaskets, valve seats and stiff overmolds. | — | 10 | 320 | 22 Shore D |
What is Silicone HCR?
Silicone HCR is Silicone in the HCR grade — pick for extruded profiles, tubing, calendered sheet and low-volume compression-molded gaskets. Silicone HCR has a tensile strength of 8 MPa (1.16 ksi), weaker than 81% of polymer grades. Elongation at break is 400% and the elastic modulus is 0 GPa (4.79×10⁻⁴ Msi). Silicone HCR has a density of 1.15 g/cm³ (0.0415 lb/in³), lighter than 57% of polymer grades. Its glass-transition temperature is -125°C (-193 °F).
Advantages
- Good UV / weathering resistance — 97/100, better than 98% of polymer grades
- Forms and bends easily — 92/100, better than 97% of polymer grades
- Polishes to a fine finish — 85/100, better than 92% of polymer grades
- High service temperature — 200°C (392 °F), better than 87% of polymer grades
- Ductile — tolerates forming and impact — 400%, better than 86% of polymer grades
Limitations
- Difficult to machine — 22/100, worse than 95% of polymer grades
- Low stiffness — 0 GPa (4.79×10⁻⁴ Msi), worse than 92% of polymer grades
- High mold shrinkage — 2.2%, worse than 87% of polymer grades
Silicone HCR properties
Typical room-temperature values for Silicone HCR; 16 are specific to this condition. Other listed values are Silicone reference data and may not represent this condition. Bars are the position among polymer grades.
Physical5
Silicone HCR has a density of 1.15 g/cm³ (0.0415 lb/in³), lighter than 57% of polymer grades. Its glass-transition temperature is -125°C (-193 °F).
Mechanical9
Silicone HCR has a tensile strength of 8 MPa (1.16 ksi), weaker than 81% of polymer grades. Elongation at break is 400% and the elastic modulus is 0 GPa (4.79×10⁻⁴ Msi).
Thermal8
Silicone HCR is rated for continuous service to 200°C (392 °F). It conducts heat at 0.22 W/m·K (0.127 BTU/hr·ft·°F), better than 60% of polymer grades. Thermal expansion is 270 µm/m·K (150 µin/in·°F).
Electrical7
Silicone HCR is an electrical insulator with a dielectric strength of 22 kV/mm (558.8 V/mil) and a resistivity of 1×10¹³ Ω·m.
Chemical & Environmental3
Corrosion resistance is excellent (90/100), better than 82% of polymer grades. UV resistance is excellent.
Sustainability4
Producing a kilogram of Silicone HCR takes about 110 MJ of energy and emits 6.5 kg of CO₂ — more than 64% of polymer grades. Typical recycled content is 0%.
Manufacturability7
Silicone HCR's machinability is poor (22/100, worse than 95% of polymer grades); weldability poor (20/100); formability excellent (92/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Silicone HCR
Is Silicone easy to machine?
Cured silicone is not conventionally machinable — use die cutting, waterjet, laser (with fume control) or cryogenic deflashing; sharp new blades and water lubrication prevent tearing.
Can Silicone be welded?
No thermal welding; join by uncured silicone adhesive, self-bonding primers, RTV, or oxygen-plasma bonding for PDMS microfluidics; secondary overmolding onto cured silicone requires primer.
Can Silicone be formed, bent or molded?
LSR: cold runner, 165–210 °C mold, 15–60 s cure, allow 2–3 % shrink and vacuum-vented tools; HCR: compression/transfer or extrusion + hot-air/steam cure; post-cure 200 °C/4 h to remove volatiles for medical/food use.
What surface finishes work on Silicone?
Surface finish is fully set by the mold (mirror EDM or texture); paints do not adhere without silicone-specific primer — use plasma/corona treatment, parylene or silicone inks; talc-free anti-block coatings for tack reduction.
Silicone chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| fumed silica (reinforcing filler)surface-treated, sets modulus and tear strength | 15 – 35 | 25 |
| hydride crosslinker (Si-H siloxane)addition-cure systems | 0.5 – 3 | 1.5 |
| platinum catalyst (Karstedt)peroxide (DCBP/DBPMH) used instead in HCR peroxide cure | 2×10⁻⁴ – 0 | 5×10⁻⁴ |
| extending filler / pigment / heat stabile.g. ground quartz, Fe2O3, Ce compounds | 0 – 15 | 5 |
| polydimethylsiloxane (PDMS) base polymermay contain vinyl-methyl and phenyl or trifluoropropyl substitution | ≥ 55 (balance) | — |
Silicone HCR — frequently asked
What is Silicone HCR used for?
Silicone HCR is typically used for O-rings and moulded gaskets, medical tubing and implant seals, keypads and button mats, baby bottle nipples and food-contact seals, electronic potting and encapsulation and high-temperature oven and appliance seals. In short: biocompatible soft silicone.
What is the tensile strength of Silicone HCR?
Silicone HCR has a typical tensile strength of 8 MPa (1.16 ksi) — weaker than 81% of polymer grades. Strength varies by condition: see the 15 listed tempers.
Is Silicone HCR easy to machine?
Not especially — machinability is rated poor (22/100, worse than 95% of polymer grades). Cured silicone is not conventionally machinable — use die cutting, waterjet, laser (with fume control) or cryogenic deflashing; sharp new blades and water lubrication prevent tearing.
Can Silicone HCR be welded?
Not readily — weldability is rated poor (20/100). No thermal welding; join by uncured silicone adhesive, self-bonding primers, RTV, or oxygen-plasma bonding for PDMS microfluidics; secondary overmolding onto cured silicone requires primer.
What surface finishes work on Silicone HCR?
Surface finish is fully set by the mold (mirror EDM or texture); paints do not adhere without silicone-specific primer — use plasma/corona treatment, parylene or silicone inks; talc-free anti-block coatings for tack reduction.
Can Silicone HCR be formed, bent or molded?
LSR: cold runner, 165–210 °C mold, 15–60 s cure, allow 2–3 % shrink and vacuum-vented tools; HCR: compression/transfer or extrusion + hot-air/steam cure; post-cure 200 °C/4 h to remove volatiles for medical/food use.
What is the maximum service temperature of Silicone HCR?
Silicone HCR is rated for continuous use to about 200°C (392 °F), and briefly to 250°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in Silicone HCR?
Yes — Silicone HCR is available for injection molding; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM D2000 — Classification System for Rubber Products (VMQ/FVMQ) — ASTM (2023)
- ASTM D412 / D624 / D395 / D2240 — tensile, tear, compression set, durometer — ASTM (2022)
- SILASTIC / Dow LSR and HCR product datasheets — Dow (2023)
- ELASTOSIL LR / R silicone rubber datasheets — Wacker Chemie (2023)
- Silopren LSR and thermally conductive silicone data — Momentive (2022)
- ASM Engineered Materials Handbook Vol. 2 — Engineering Plastics/Elastomers — ASM International (1988)
- CAMPUS / UL Prospector elastomer entries — UL / CAMPUS (2024)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.